A promising technique for isotope separation, and more particularly for uranium enrichment, operates by the application of laser radiant energy in preferably two or more photon wavelengths to a vapor flow of the uranium particles in such a manner as to selectively photoionize the uranium particles of one isotope type without corresponding photoionization of particles of other isotope types. The selectively photoionized particles are then typically accelerated onto trajectories for separate collection by application of crossed-field magnetohydrodynamic techniques. The plural isotopes of uranium may typically be vaporized from an elemental state by heating to produce a particle flow into the region of selective photoionization and beyond. See, for example, U.S. Pat. No. 3,772,519.
In providing an efficiently operative system according to this principle, a trade-off may be balanced between the rate of uranium evaporation and corresponding particle flow density and the loss in efficiency resulting from atom-atom scattering and from charge exchange reactions. Atom-atom scattering involves particle flow deflections as a result of collisions and charge exchange reactions occuring between neutrals and selectively ionized particles to permit loss of desired particles and collection of undesired particles. Both of these effects become more damaging as the particle flow density increases. In addition, since the crossed-field magnetohydrodynamic forces are applied to all charged particles in the environment, particles which have become ionized through processes other than selective photo-ionization will be deflected and collected along with the enriched uranium isotope thereby also diluting the yield. Moreover, particles may exist in the particle flow in excited but un-ionized states and thus fail to be photoionized unless additional laser frequencies are employed.